1. Field of the Invention
The present invention relates to apparatus for use in oil and gas wells or the like, and particularly to selective injection packers of the type having a pair of longitudinally spaced packers and having an injection port located between the packers.
2. Description of the Prior Art
It is often necessary to selectively treat relatively short perforated intervals in oil and gas wells while isolating the treatment area from other intervals in the well bore. For example, this may be done for the purpose of washing the perforations or for injecting treatment chemicals into the formation.
Furthermore, it may be desirable to isolate such short intervals for the purposes of testing flow and/or pressure at various levels of a particular producing formation in order to ascertain whether there is damage to some or all perforations or the formation, whether it is desirable to treat the entire formation in some manner, or whether only certain intervals need be subjected to treatment.
There are a number of ways to accomplish these operations. For example, a bridge plug and a packer may be set below and above the interval, respectively, and the interval then treated through the packer. This has the disadvantage of requiring setting and unsetting of two tools for each treatment or test interval.
Alternatively, a straddle-type packer having two sealing elements may be employed. Such straddle-type devices may have sealing elements which are compressible, inflatable or expandable (cup-type).
Inflatable elements require relatively complex valving, particularly if it is desired to set and unset the tool a number of times. In addition, such tools are long and bulky, and in many cases require fairly precise control of tubing pressures for inflation, as well as separate inflation channels or lines.
Cup-type elements are severely restricted in the amount of pressure they can contain, are susceptible to severe frictional wear in deep holes, and require a bypass around the cups if it is desired to reverse-circulate in the well bore.
Compressible packer elements possess advantages over other types of packer elements, but most tools employing compressible packer elements are weight-set, thereby restricting their use to deeper wells and often preventing their exact location at a particular interval.
The present invention relates to a straddle-type packer of the type having compressible packer elements which are hydraulically set. An example of a prior art device having hydraulically set compressible packer elements is shown in U.S. Pat. No. 2,715,444 to Fewel. In the Fewel device, a pair of pistons are operated by tubing pressure to longitudinally compress and radially extend a pair of spaced compressible type packers to seal the packers against the well bore. Then, tubing string weight is slacked off to set down a mandrel portion of the device and move it longitudinally relative to a housing which is attached to the packer elements, to open an injection port located between the packer elements.
The present invention provides a number of improvements in devices of the type generally shown in the Fewel patent.